Pros Fight Glare, Poor Color Quality in Stadium Lighting

Do you think San Francisco Giants outfielder Barry Bonds could have hit 73 homes during the 2001 Major League Baseball (MLB) season with his eyes closed? Or that Ed McCafferty of the Denver Broncos could catch a Brian Griese pass in the dark?

Consider this: a Randy Johnson fastball traveling at 90 miles per hour covers the distance between the pitcher’s mound and the batter in less than one-half second. At that speed, the tiny white projectile looks like an aspirin tablet. Though Bonds is blessed with 20/20 vision, excellent reflexes, and lighting-quick bat speed, he would be just another hacker if Pacific Bell stadium was equipped with anything less than state-of-the-art lighting fixtures.

Rosendin Electric of San Jose and Dynalectric of Lakewood, Colo., faced two challenges while installing lighting fixtures at the new homes of the Giants and Broncos, besides those of running wires and conduit to the metal halide lamps installed at the parks:

The conversion to metal halide lights in the industry has been evolutionary, as manufacturers have struggled to produce efficient, high-wattage lamps and fixtures. Metal halide is preferred in indoor and outdoor facilities because it produces white light. Plus, the lamps achieve 4,000-degree Kelvin color temperature, so color rendition is approximately 65 percent. After two seasons at Pacific Bell and one Monday Night Football broadcast in Denver, MLB and the National Football League are satisfied with broadcast quality.

Among the first steps in the process was the design of light zones with different levels of illumination. At Pacific Bell, for instance, different specifications were designed for the pitcher-catcher zone, infield, midfield, outfield, and “celebrity zone” in the first dozen rows of seats behind home plate between the dugouts.

With lamps placed 170 to 180 feet above the playing fields, Pacific Bell was illuminated with 556, 2,000-watt lamps; 664, 1,500-watt lamps were installed at the 70,000-seat facility in Denver.

“Aiming the lights from the towers actually proved to be less challenging than we had anticipated. The fixtures are furnished with rifle-type sights that we used to aim each fixture at grid-coordinate points down on the field that the manufacturer’s computer program generated,” said Barry Boehm, project manager for Rosendin Electric.

Newer lamps have a different design and shielding than traditional metal halide lamps with bulb jackets and mogul base sockets. Critics say the old designs produce inefficient symmetrical light distribution, with too much light in the upper beam. The result is light lost in the sky and grandstands, or areas outside the stadium. Newly developed bulbs are tube shaped and have no jacket. This allows placement of the lamp arc in the focal point of the shallow parabolic reflector forms needed to build high center beam candlepower, increasing beam efficiency.

Older fixtures with external visors reflect light downward, but are less efficient and also produce wind loading. The newer ones have internal reflectors that place the lamp arc in the focal point of shallow reflector forms to produce high center beam candlepower.

Rear reflectors in some fixtures are press-molded glass that one manufacturer claims have 95 percent light reflectivity. The front reflector is specular aluminum.

The new lamp-reflector combination produces an oval light distribution pattern with tight vertical lighting controls. So, less light is wasted and more is on the target. Depending upon wattage, the bulbs have a life span between 3,000 and 10,000 hours.

The bottom line is that high-wattage lamps require fewer fixtures. This leads to lower installation, structural, maintenance and energy costs.

Since many of these stadiums are being built as the centerpiece of urban areas surrounded by office/residential complexes, environmental issues are a high priority. A major challenge is reducing off-site light pollution produced by light reflected from glass windows and panels, so fixtures and architectural designs produce better shielding. Shields in the fixtures reduce pollution, as do walls and canopies built around the fixtures.

To reduce power consumption, the systems in both stadiums were designed with multi–level controls that reduce lighting during practices and maintenance periods.

Plus, units at Denver were equipped with instant hot restart ballasts that work in two seconds, once power is restored. Old lamps required eight to 12 minutes.

In the future, you can look for color rendition improvements that will equal our European counterparts’, but at less cost. EC

LAWRENCE is a freelance writer and photographer based in Bozeman, Mont. He can be reached at hrscrk@mcn.net.